ALung Technologies, Inc. is developing a respiratory catheter (the Nattier Catheter) for treatment of acute and acute-on-chronic respiratory failure, which affects over 100,000 adults in the United States. A major limitation in clinical respiratory catheters and other implantable artificial lungs being developed is that commercial hollow fiber membranes (HFMs) wet after only a few hours of blood contact. In wetting, blood plasma fills the fiber wall pores and the fiber gas permeance decreases substantially causing insufficient gas exchange. This poses a serious problem because the fibers of implantable artificial lung devices cannot easily be replaced. Thus, for effective clinical use an implantable artificial lung must contain non-wetting HFMs that retain sufficient gas exchange characteristics. Phase I Goals -1) Develop non-wetting HFMs with high gas permeance. Gas-plasma phase polymerization will be used to create an ultra-thin but continuous layer of polymer with high gas permeability, sufficient to prevent liquid intrusion but thin enough to accommodate with negligible diminution the required gas exchange rates; and 2) Bench tests of candidate HFMs designed to evaluate wetting resistance and gas permeance. Tests will be performed in simple modules of candidate fiber samples throughout the optimization process. The best candidate fiber will be incorporated into the Hattler Catheter and evaluated in bench water and blood gas exchange tests. Phase II - Focuses on increased thromboresistance of fiber coatings. Polymers investigated in Phase I are generally more biocompatible than uncoated fibers, but the need for minimizing anticoagulation warrants exploring further improvements in the biocompatibility. The fibers emerging from this program will be of promise for artificial lung devices being developed for patients with lung failure.